Draft regulator



F141 zo m F142 v @I Jan. 29, 1935. .1. c. MILES 1 1,989,105

' DRAFT REGULATOR Filed Aug. 31, 1933 anew M 4 Patented Jan. 29, 1935 UNITED STATES PATENT OFFICE 9 Claims.

This invention relates to heating apparatus and particularly to forced draft appliancesthat are used for controlling the combustion of fuel in a furnace. Forced draft units usually include a motor and a blower with control apparatus for automatically shutting offthe motor, either when the room temperature reaches the desired degree, or before the furnace temperature reaches a degree that is regarded as unsatisfactory for safe operation. 5

Heretofore forced "draft units have been provided with control apparatus that would stop the operation of the blower, whenever the temperature of the water or air heated by the furnace or in the use of a boiler whenever the pressure reached a predetermined degree. Where a'blower is used however, the fire builds up quickly, with the result that the furnace temperature reaches the dangerous point long before the desired room temperature is obtained. Thus, the blower is operated intermittently many times during the process of bringing the room temperature up to the desired degree. The intermittent operation of the blower is highly objectionable however, for whenever the source of air supply to the furnace is suddenly discontinued, the ash just above the grate forms a solid bed of clinker that hinders the passage'of'air through the fuel.

A further objection to the intermittent operation of the forced draft unit is the fact that the blower for each installation has a size that cor-' responds to the peak-load capacity of the furnace. Accordingly, whenever the, blower is operated, it is furnishing enough air for peak-load capacity and so it follows that when the blower is suddenly stopped, the fuel has acquired a .combustion rate that cannot be suddenly checked whenever the blower is stopped. As a result the temperature, or the pressure, as the case may, of the heating medium exceeds the desired degree, and the operation of the blower is not resumed until the temperature or pressure drops a predetermined amount below the desired degree. In. the meantime, air is being supplied to the fuel only through cracks adjacent the fire door opening, and hence the fuel is inefllciently burned.

An object of my invention therefore, is to provide a control apparatus, wherein the blower is continuously operated so long as the room temperature or pressure is below the desired degree, but wherein provision is made for gradually varying the volume of air entering the furnace, so as to maintain a substantially constanttemperature or pressure of the heating medium in the region of the furnace. In this way, the constantly moving current of air keeps the ash cool and prevents the formation of clinker, and thus keeps the furnace operating at maximum efficiency.

Referring now to the drawing, Fig. 1 is a sectional view through a hot air furnace, embodying my invention; Fig. 2 is a side elevation of a steam boiler, having my invention associated therewith; Fig. 3 is a longitudinal vertical section through the draft control unit on a larger scale than that used in Fig. 1; Fig. 4 is a section takenon the line 4-4 in Fig. 3; Fig. 5 is a side elevation of the control apparatus.

Referring first to Fig. 1, 10 indicates the furnace, 11 indicates the ash pit, 12 indicates the bonnet and 13 indicates the casing of a hot air furnace. -My invention includes a draft unit for supplying air to the furnace through the ash pit, and so I have indicated such unit, as comprising a motor 15 which operates a blower 16. The motor and blower are directly connected, and are mounted preferably on the top of the draft conduit 17, which extends through a passageway in the casing 18 and terminates adjacent an opening 19 in the ash pit. A standard, shown as a pair of plates 65, may be used to support the air conduit. A room-thermostat 20 may be used to control the motor by closing the circuit through it whenever the temperature in the room falls below that at which'the thermostat is set and by interrupting the current, whenever the temperature reaches the predetermined degree. Thus the blower is operated continuously so long as the room temperature is below the required'degree.

If the blower were operated continuously so long as the. room temperature is lower than that at which the thermostat is set, it is obvious that the temperature or pressure of the heating medium would rise to a prohibitive amount, and so I have provided a draft control-apparatus that automatically and gradually varies the amount of air that can be admitted to the furnace, not withstanding the fact that the blower is operated continuously. The draft control apparatus, which I prefer to utilize includes a damper 30 that is so mounted within the conduit 17 as to swing about a pivot 31, and that is normally closed by the action of gravity, but is capable of being forced open by the pressure of air flowing from the blower. I

In the. preferred arrangement-the air conduit on the inlet side of the damper is shorter in depth than on the discharge side ofit. Thus, a

substantial amount of air may be permitted to flow past the damper, even though the damper I is moved only a short distance from the normally closed position. This permits a very delicate control, and enables a steam pressure to rigidly mounted on a pivot 39 that extends across is supported within a retaining bracket 42, and

the draft conduit on'the discharge side of the damper. The pivot is journalled in the side walls of the conduit, and has one end thereof projecting outside the wall. As is shown in Fig. 4, an arm 40 is rigidly connected to the pivot, and is arranged to be moved in accordance with the degree of temperature or pressure of the heating medium adjacent the furnace.

In the case of a hot air furnace, one end of the arm 40 is attached to a collapsible bellows 41 that that communicates through a pipe 43 with'a reservoir 44 in the bonnet of the furnace. An expansible fluid fills the reservoir pipe and bellows,

and as the pressure in the collapsible bellows is increased, the arm 40 is moved in a direction to close the damper against the pressure of air from the blower. The extent of movement can be controlled by the position of a weight 45 on the arm 40. This same arrangement can be utilized for a hot water boiler, for in such case, the reservoir 44 would be placed inside the boiler and in contact with the water.

In the case of a steam or vapor boiler, as is shown in Fig. 2, I prefer to make a direct con.-

nection between the usual ashpit door draft control arm 50, and the damper control arm 40 by means of a chain 51. In such case, the adjustment of a weight 52 on the draft control arm 50 will be suflicient to provide the desired degree of adjustment.

The operation ,of the apparatus embodying my invention is as follows: Assuming that the room thermostat temperature falls below the normal desired room temperature, then the circuit is closed through the motor and the blower is operated to force air into the furnace through the ash pit. In the case of a hot air furnace, whenever the temperature in the bonnet reaches a predetermined degree, which is set for safe operation, the expansible fluid in the thermostat 44 expands the bellows 41', thus moving the arm 40 and arm 38 in a direction to close the damper. Such motion is very gradual and as a result, the

furnace is gradually checked, thus insuring efilcient combustion until the room temperature reachesthe desired degree. At such time, the room thermostat interrupts the current" to the motor, and stops the blower. The damper 30 then falls by gravity into the closed position and remains in such position until the blower is again operated. Thus, the flre as automatically checked, until the room thermostat shows an indication for additional heat. g In the case of asteam boiler when the pressure reaches apredetermined degree, the expansible and collapsible bellows 60 moves the draft arm 50, chain 51 and thence arm 40 to resist the opening movement of the damper and gradually moves it to closed position. This automatically checks the fire and yet sustains a combustion rate that will maintain the predetermined pressupply of air to the furnace so long as the room temperature is below the desired degree. The air is supplied in just the proper portion to maintain the most efficient operation of the furnace, and thus the fuel is compl'etelyconsumed in the most eflicient manner.

While I have described my invention in connection with a furnace that is used for heating a room in which a thermostat is located, I may, if desired, use it in connection with the operation of a hot water heater, in which case the temperature of the water to be heated constitutes the heating medium, the temperature of which is utilized for actuating the mechanical apparatus to close the damper against the pressure of air that tends to open it. The constantly acting air pressure being opposed by mechanical pressure and the mechanical pressure being responsive to changes in the physical condition of the heating medium provides an arrangement which is extremely sensitive and enables one to maintain an accurate control of the temperature or pressure of the heating medium within hitherto unaccomplished limits. In case coal is used as the fuel, the furnace may be completely filled with coal and thereafter the apparatus will operate automatically to supply air in just the exact proportion to maintain a predetermined temperature or pressure of the heating medium. This has resulted in an important saving in fuel for it enables one to utilize a lower grade of fuel for a given furnace. Furthermore, it minimizes the attention that is necessary to maintain a uniform temperature or pressure and thus accomplishes with comparatively inexpensive apparatus better results than an expensive stoker.

I claim: 7 1

1. In combination, a furnace, a blower for supplying air to support combustion, an air conduit extending from the blower to the furnace, a

damper in the conduit and normally closed by gravity but adapted to be opened by pressure of air from the blower and a device responsive tomeans for supplying air to support combustion within the furnace, a damper for controlling the volume of air entering the furnace and an expansible actuator responsive to changes in temperatures in the heating medium of the furnace for resisting the opening movement of the damper, said actuator being adapted to close the damper against the pressure of air whereby the volume of air admitted to the furnace is controlled automatically in accordance with the rate of combustion required to maintain a substantially constant temperature or pressure of the heating medium. I

3. In combination, a furnace, a blower, a conduit for conducting air from the blower to the furnace to support combustion therein, a damper within the conduit, the damper being normally closed by gravity but adapted to be opened by the pressure of air from the blower,- and means influenced by changes in the physical condition of the heating medium for opposing movement of the opening of the damper whereby the position of the damper is automatically controlled-to maintain constant physical condition of the heating medium in the region of the humane.

4. In combination, a thermostat in a room'to be heated, a furnace, a thermostat in the region of the furnace and in the medium through which the heating is accomplished, a motor driven blower for supplying air to the furnace to support combustion, a conduit leading from the blower to the furnace, a damper within the conduit, the damper being normally urged in one direction by the pressure of air from 'the blower and being urged in the opposite direction by the temperature responsive device in the region of the furnace, whereby the damper is automatically moved to supply the correct amount of air for supporting combustion so as to maintain the temperature of the heating medium adjacentthe furnace at a substantially constant degree so long as the temperature in the room to be heated is below that at which the room thermostat is set.

5. In combination, a hot air heating furnace, a conduit for supplying air to the furnace for supporting combustion therein, a motor and a blower associated with the conduit, a damper within the .conduit and being normally moved to closed position by gravity but adapted to be moved toward the open position by pressure of air from the blower, a second member pivotally mounted within the conduit and disposed on the side of the damper opposite the blower and being adapted to engage it, a temperature responsive device disposed in the bonnet of the furnace, and means actuated by said device for operating said member to resist movement of the damper under the influence of the air from the blower, whereby the position of'the damper is automatically varied so as to support combustion at the proper rate to maintain-substantially constant temperature within the bonnet of the furnace.

8. In combination. a furnace, a heat conveying medium heated thereby, a conduit leading to the furnace for supplying air to support combustion within the furnace, a damper in-the conduit, means for forcing a current of air under pressure into the conduit, the air pressure acting against one side of the damper and tending to open it, mechanically actuated means acting against the other side of the damper and tending to close it, said mechanically actuated means being responsive to changes in the physical condition of the heating medium.

"I. In combination, a hot air furnace, a conduit leading to the furnace for supplying air to support combustion therein, a damper carried by the conduit, means for supplying air under pressure to the conduit, the air pressure acting against one side of the damper and tending to open it, mechanism acting against the other side of the damper and tending to close it, and means responsive to changes in temperature of the air that is heated by the furnace for actuating said mechanism.

8. In combination, a hot water boiler, a conduit leading thereto for supplying air to support combustion therein, a damper in the conduit, means for supplying 'air under pressure to the conduit, the air pressure acting against one side of'the damper and tending to open it, mechanism acting against the other side of the damper and tending to close it, and means responsive to changes in temperature of the water heated in the boiler for actuating said mechanism.

9. In combination, a steam boiler, a conduit leading thereto for supplying air to support combustion therein, a damper in the conduit, means for supplying, air under pressure to the conduit, the air pressure acting against one side of the damper and tending to open it, mechanism acting against the other side of the damper and tending to close it, and means responsive to changes in pressure of the steam in the boiler for actuating said mechanism.

, JAMES C. MILES. 

